Week 5: Parasitology Part II Flashcards
learning objectives
For the parasitic organisms identify
- the geographical region of risk
- mode of transmission
- Life-cycle
- clinical symptoms
- clinical complications of infection
- laboratory diagnostic tests
- appropriate treatment
- side effects of treatment
Case 1
Question
D. Schistosoma japonicum
Schistosomiasis Life-cycle
- Infected person (Reservoir) releases trematode eggs in urine or stool
- Eggs contaminate freshwater
- Eggs hatch and infect snails (intermediate host) and divide
- Free swimming cercariae released into the water and penetrate human skin
People defecate oocytes which enter freshwater and eggs hatch and infect snails and divide, the snails release free-swimming cercariae into the water which penetrate human skin
Cercariae lose tails during penetration and become schistosomulae and enter the circulation and migrate to the portal blood in liver and mature into adult worms that perform sexual reproduction
Paired adult worms migrate to mesenteric venules of bowel/rectum laying eggs that circulate to the liver and are shed in stools to infect more snails
Schistosomiasis pathophysiology
eggs can migrate to the liver to be shed in stools or to other tissues such as wall of intestine or liver (mansoni or japonicum), bladder wall (haematobium) -> granulomas -> fibrosis
Liver Schistosomiasis
- Schistosoma mansoni
- Schistosoma japonicum
Bladder wall fibrosis Schistosomiasis
Schistosoma haematobium
Clinical manifestations of Schistosomiasis
- Swimmer’s itch: Cercariae penetrating skin (pruritic papular rash after penetration)
- Katayama fever (Acute schistosomiasis)
- systemic hypersensitivity reaction to Schistosoma antigens occurring 1-2 months post-exposure
- Fever, chills, cough, urticaria, angioedema, arthralgias, dry cough, abdominal pain, lymphadenopathy, and splenomegaly
- Massive eosinophilia
- Deposited eggs cause granulomas & fibrosis
- periportal fibrosis/portal hypertension
- Hematuria and bladder cancer
Would you predict that a patient with Schistosomiasis would have eosinophilia?
Yes, during swimmer’s itch phase and especially during the Katayama fever.
The granulomatous stage doesn’t have a big immune response
What laboratory test to diagnose Schistosomiasis
- Stool test if it is in the liver and biliary system
- Urine for bladder
Schistosoma species
- Schistosoma mansoni
- Schistosoma haematobium
- Schistosoma japonicum
Schistosoma mansoni region
- Africa
- South America
- Carribean
Schistosoma mansoni eggs found in
- Stool
Schistosoma haematobium region
- Africa
- Middle East
Schistosoma haematobium eggs found in
Urine
Schistosoma micro egg exam
Schistosoma mansoni micro egg exam
Schistosoma japonicum region
- Indonesia
- China
- SE Asia
Schistosoma japonicum eggs found in
Stool
Schistosoma japonicum micro exam of eggs
Schistosomiasis treatment
Praziquantel
Praziquantel MOA
Kills adult schistosomes and causes them to become dislodged from mesenteric, hepatic or pelvic veins -> phagocytosed in liver
Kills adult worms (does not kill eggs or treat fibrosis)
Praziquantel best used when?
During acute schistosomiasis (single dose 6-8 weeks after last exposure to potentially contaminated freshwater)
Praziquantel side effects
Majority of side effects develop due to host immune reaction to killed parasites (release lots of antigens when they die)
Examples of Trematode infections
- Schistosomiasis
- Paragonimus westernmani
- Clonorchis sinensis
- Fasciola hepatica
Paragonimus westernmani region
SE Asia
Paragonimus westernmani AKA
Lung fluke
Paragonimus westernmani transmission
ingestion of undercooked crabs/crayfish contaminated with metacercariae
Signs & symptoms of Paragonimus westernmani
- Lung cyst rupture
- Chronic bronchitis
- TB-like picture
Paragonimus westernmani diagnosis
- eggs in sputum
- serology
Paragonimus westernmani Tx
Praziquantel
Clonorchis sinensis region
Asia
Clonorchis sinensis AKA
Liver fluke
Clonorchis sinensis transmission
ingestion of undercooked freshwater fish contaminated with metacercariae
Signs & Symptoms of Clonorchis sinensis
- obstructive jaundice
- biliary strictures
- pigmented gallstones
- cholangitis
- cholangiocarcinoma
Clonorchis sinensis Dx
Eggs in stool
Clonorchis sinensis Tx
Praziquantel
Would becoming a vegetarian eliminate the risk of intestinal parasite infection?
No, for example Fasciola hepatica
Biliary strictures & cholagniocarcinoma and Hx of undercooked fish
Clonorchis sinensis
Undercooked crab/crayfish
Clonorchis westernmani
Fasciola hepatica region
Worldwide trematode
Fasciola hepatica AKA
Common Liver Fluke
Common Liver Fluke
Fasciola hepatica
Fasciola hepatica definitive host
Sheep/cattle
Fasciola hepatica intermediate host
Snail
Fasciola hepatica Incidental host
Human
Fasciola hepatica transmission
ingestion of raw watercress or other plants contaminated with metacercariae -> migrate through duodenal wall -> peritoneum -> liver -> biliary ducts -> obstruction
Fasciola hepatica Dx
Eggs in stool or duodenal or biliary aspirated
Fasciola hepatica Tx
Triclabendazole
Triclabendazole caveat
Not FDA approved so must obtain from CDC
Case 2
Question
C. Taenia solium
Taenia solium type
Helminth: Cestode/tapeworm
Taenia solium Intermediate host
pig
Taenia solium definitive host
human
Taenia solium transmission
- Human ingestion of larval cyst in undercooked pork causes Taeniasis (intestinal infection) with adult worms -> excrete eggs in stool
- Human ingestion of eggs from fecal-contaminated water or vegetation causes Cysticercosis (tissue infection)
Human ingestion of larval cyst of Taenia solium
Taeniasis (tape-worm intestinal infection)
Human ingestion of larval cyst of Taenia solium
Cysticercosis (tissue infection)
Describe the life cycle of Taenia solium
- pigs ingest fecal-contaminated feed
- oncospheres hatch and penetrate pig intestinal wall and circulate to the musculature
- Oncospheres develop into cysticerci in pig muscle
- Humans infected by ingesting undercooked or raw infected meat
- Taeniasis: Scolex attaches to intestines and grows to adults in small intestine
- Cysticercosis: oncospheres hatch penetrate the intestinal wall and circulate to musculature, cysticerci may develop in any organ being more common in subcutaneous tissues as well as in the brain and eyes
Tenia solium Dx
- Imaging
- serology
Tenia solium Tx
Praziquantel x 1 (cysticidal)
Albendazole (cysticercosis)
or may not need treatment
Diphyllobathrium latum AKA
Fish tapeworm
Diphyllobathrium latum transmission
Ingestion of undercooked freshwater fish
Diphyllobathrium latum signs & symptoms
competes for vit B12 in host intestine -> macrocytic anemia
Diphyllobathrium latum Dx
eggs in stool
Diphyllobathrium latum Tx
Praziquantel
An infection with which cestode can lead to hydatid cyst in the liver or lung?
Echinococcus
How does a patient become infected with Echinococcus?
How is Echinococcus Dx’ed?
- Imaging to see hydatid cyst
- Serologies
- Never aspirate hydatid cyst because can cause anaphylactic shock
Who commonly gets Echinococcus?
Raw food or food infected with dog feces (Sheep herders commonly get Echinococcus)
Case 3
Do you aspirate hydatid cyst?
No, can cause anaphylactic shock
Question
C. Stool Ova & Parasite
Case 3 Stool sample
Strongyloidiasis
Question
C. Strongyloides stercoralis
Strongyloides stercoralis stool and blood agar
Describe the life-cycle of Strongyloides stercoralis
- Rhabdiform larvae in the intesine are excreted in stool and
- autoinfect
- but also develop into free-living adult worms that perform sexual reproduction
- eggs are produced by fertilized female worms
- Rhabditiform larvae hatch from embryonated eggs
- The rhabditiform larvae develop into infective filariform
- Infective filariform larvae penetrate the intact skin initiating the infection
- The filariform larvae enter the circulatory system and are transported to the lungs and penetrate the alveolar spaces, they are carried to the trachea and pharynx, swallowed and reach the small intestine where they become adults
- Autoinfection rhabditiform larvae in large intestine become filariform larvae, penetrate intestinal mucosa or perianal skin and follow the normal infective cycle
- Eggs deposited in the intestinal mucosa hatch and migrate to the lumen
- Rhabditiform larvae in the intestine are excreted in stool
Describe the initial infection of Strongyloidiasis
Filariform larvae penetrate the skin -> migrate through tissue into blood -> to lungs -> into alveoli -> trachea -> cough up and swallow -> in intestine -> can cross intestine wall (perforation) to peritoneum
Strongyloidiasis signs & symptoms of initial infection
Skin
- Intense pruritis at site of skin penetration
Lungs
- Transient fever, cough and wheezing
GI
- symptoms only if lots of worms
- abdominal pain, vomiting, diarrhea
- Perforation with peritonitis from GI flora
Strongyloidiasis signs & symptoms of autoinfection
- Larva currens: peri-anal serpiginous urticarial rash
- can lead to chronic infection for decades
- Hyperinfection syndrome: Autoinfection in immunocompromised patients, Abdominal pain, diffuse pulmonary infiltrates, septicemia or meningitis with GNR
Describe autoinfection of Strongyloidiasis
female worm lays eggs in human bowel wall -> larva hatch -> larval invasion of perianal skin
Strongyloidiasis stercoralis Dx
Stool & blood agar
In the stool: Rhabditiform larvae in stool, sputum, CSF, other body fluid
Stool culture shows GNR along the track of movement of larvae
Strongyloidiasis Tx
- Ivermectin x 1
- Second line: Albendazole x 7 days
Ascaris lumbricoides type
Nematode/round-worm
Ascaris lumbricoides transmission
Fecal-oral
Ascaris lumbricoides infection type
Intestinal infection
Ascaris lumbricoides Dx
Eggs in stool
Ascaris lumbricoides Tx
- Albendazole
- Mebendazole
Ascaris lumbricoides overview
Describe the life-cycle of Ascaris lumbricoides
- Ingestion of eggs in fecal-contaminated food
- egg releases larval worm which penetrates duodenum
- Carried in bloodstream to pulmonary circulation
- Larvae break free in alveoli where they mature over 3 weeks
- Coughed up and swallowed
- Adults mature in intestine & copulate and release eggs in stool
Necator americans region
New world
Ancylostoma duodenale region
Old world
Necator americans description
Roundworm “hookworm”
Necator americans distribution
Tropics, subtropics
Necator americans Transmission
Contaminated soil -> larvae penetrate through skin
Necator americans definitive host
humans
Necator americans clinical syndrome
- cutaneous larva migrans & eosinophilia: Pruritic maculopapular rash at site of penetration
- Nausea, vomiting, diarrhea, abdominal pain
- Anemia: sucks blood from intestinal wall
Necator americans Dx
Detection of eggs in stool
Necator americans Tx
Albendazole
Describe the life cycle of Necator americans
- eggs in feces, rhabditiform larva hatches
- larva in fecal-contaminated soil in the tropics/subtropics become filariform larva
- filariform larva penetrate the skin from walking barefoot and migrates through blood vessels to lungs
- larva penetrate alveoli and ascend to pharynx and are swallowed (transient pulmonary symptoms)
- become adult worms in intestines and perform sexual reproduction and cause anemia in host
- Are released in feces
Necator americanus analogous in old world
Ancylostoma duodenale
Trichuris trichuria type
Nematode
Trichuris trichuria exposure
soil containing eggs
Trichuris trichuria clinical syndrome
whipworm: tenesmus, rectal prolapse
Trichinella type
Nematode
Trichinella exposure
Ingesting contaminated food (pig, bear)
Trichinella clinical syndrome
- mild diarrhea
- periorbital edema
- myalgias
Dracunculus mediensis description
nematode
Dracunculus mediensis exposure
ingestion of contaminated water
Dracunculus mediensis clinical syndrome
Guinea worm: malaise, fever, adult worm emerges
Dracunculus mediensis type
Nematode
Enterobius vermicularis type
nematode
Enterobius vermicularis exposure
Fecal-oral
Enterobius vermicularis clinical syndrome
- intestinal pinworm
- anal pruritis
Loa Loa type
Nematode
Loa Loa exposure
- Deer fly
- Horse fly
Loa Loa Clinical syndrome
- Conjunctival worm
Onchocerca volvulus type
Nematode
Onchocerca volvulus exposure
Female blackfly bite
Onchocerca volvulus clinical syndrome
River blindness
Toxocara canis type
nematode
Toxocara canis exposure
fecal-oral
Toxocara canis clinical syndrome
visceral larva migrans
Wuchereria bancrofti type
nematode
Wuchereria bancrofti exposure
female mosquito
Wuchereria bancrofti clinical syndrome
Elephantiasis (lymphatic filariasis)
